Control systems are employed in many applications where the input to a subsystem (referred to as the “plant” herein) has to be generated such that its output (one or more physical, measurable quantities) follows a desired value over time, even in the presence of disturbing influences on the subsystem. This desired value of the system output represents the input to the entire control system and is referred to as “desired system output” or in the description of an implementation example as “command position signal” herein.
The generation of the controlling input signal to the plant can be optimized to generate the desired output with high bandwidth, low error or some other optimization criterion. At the same time, it may be desirable to optimize suppression of disturbing influences on the plant. Optimization for more than one of these criteria can generally not be achieved and the resulting implementation necessarily represents a compromise.
Control systems are typically implemented in a closed-loop configuration where the output of the subsystem to be controlled is measured and compared to a desired system output. The difference between desired and measured system output constitutes the “error”, which is used to generate the input to the controlled subsystem.
The use of a measure of the system output signal to generate the controlling input to the plant creates a signal-flow loop. Systems containing such loops are subject to stability limits, i.e. the components of the loop have to satisfy certain criteria to ensure stability of the loop and thus controllability of the system. These criteria impose additional constraints on the optimization of the system implementation.
What is needed are systems and methods for improving control system bandwidth that do not constrain optimization for the other criteria mentioned and do not affect the stability of the closed-loop system.